1. Field of the Invention
This disclosure relates to battery charging systems, and, more particularly, to rechargeable battery charging systems.
2. Description of the Prior Art
Rechargeable batteries have been widely used in many different applications, and many different types of rechargeable batteries have been developed including, but not limited to, nickel-cadmium, nickle-metal-hydride, lithium, and lead acid. As batteries are charged some batteries are damaged if they are over charged. For instance, in some types of batteries crystals may form which interfere with the battery's ability to store a charge, and the battery's ability to supply voltage or current.
Another common problem when charging batteries is overheating the batteries. When a battery overheats during charging or as a result from overcharging, the structures inside the battery may become deformed, and the battery will have a reduced life, a reduced ability to store a charge, and reduced ability to supply voltage or current.
As batteries may be damaged if not charged properly, battery chargers are typically designed to charge one type of battery even if the charger has the ability to charge multiple batteries, all batteries must be the same type. If multiple types of batteries need to be charged, multiple battery chargers must be purchased.
Some battery chargers are pre-set to deliver a constant current to a battery for a specific period of time. Some chargers include a sensor to shut off the battery charging process when the battery has reached a specific voltage. Other chargers measure voltage of the battery and charge the battery at one voltage until a certain voltage is reached and then charge the battery at a different voltage for a period of time.
Each battery manufacturer recommends conditions for charging their battery, as the characteristics of one battery manufacturer to another are different, even for the same type (i.e. nickel-cadmium) of battery. Some manufacturers recommend a low voltage or low current charge after the complete charging of the battery to maintain the battery at full capacity before the battery is put into use.
Other methods of maintaining a battery include a pulse method where current is not continuous, but periodic to maintain the battery. Separate systems from the charging system are often used to maintain the battery at full capacity.
In applications where batteries are used in a regulated industry, or where reliability is very important, testing of batteries also must be done to ensure that the battery can perform as needed. Testing equipment is used in regulated industries, such as the airline industry, to verify and certify the ability of a battery. The testing equipment is typically separate from the charging equipment and the maintenance equipment.
Testing equipment may also be specific to a certain manufacturer because the characteristics of batteries from one manufacturer may be different than those from a different manufacturer. If batteries from multiple manufactures need to be tested, multiple sets of test equipment may be needed. As batteries in some industries need to be charged, tested, and maintained, and batteries are from multiple manufacturers, a large amount of equipment is typically needed to fill these needs.
Typically battery chargers are set to deliver a specific amperage value (current) to the battery over a specific period of time. The battery has some resistance and according to Ohm's law, the current (I) is equal to the voltage (E) divided by the resistance (R), or I=E/R. If the current is fixed and the resistance of the battery does not change during the charging cycle then the voltage will not change during the charging cycle. However, the resistance of the battery does change during the charging cycle, and may increase depending on the temperature of the battery and the amount of charge in the battery.
As the temperature of the battery increases, the resistance increases. According to Ohm's law, for the current to stay the same when the resistance increases the voltage must also increase. The increased voltage across battery when charging may increase the temperature of the battery, and the resistance of the battery. As the temperature of the battery increases, the battery may be damaged from overheating. The battery may also become overcharged.
When batteries are overcharged they are damaged. For example, nickel-cadmium batteries react to heat by forming crystals inside the battery. When a battery is charged the electricity effects a chemical reaction inside the battery, thereby “storing” electricity. When a battery is overcharged much of the electricity flowing into the battery is dissipated as heat instead of effecting a chemical change in the battery. Whether from overcharging or from charging too quickly, when a battery heats up crystals form which interfere with the chemical process. As these crystals become larger and more numerous from repeated overcharging and overheating, the battery is not able to efficiently deliver current as needed and is no longer useful.
The general intent with a battery charger is to recharge a battery to full capacity so that the battery can be used as many times as possible. Systems to maintain batteries are used as it is desirable to have a battery at full capacity when needed. Batteries will perform better if the charging and maintenance is based on the specific characteristics of the battery. As there are many different types of batteries, individual batteries will have their own specific charge time based of the battery condition, and the batteries of the same type may vary depending on the manufacturer. Further, batteries of the same type manufactured by the same manufacturer at the same time may vary in characteristics.
Therefore, it is desirable to have a battery charger that may be adjusted to meet the needs of charging for a specific battery as well as the specific needs to maintain the battery. It is also desirable to have a battery charger with multiple channels which can each be adjusted to meet the needs of a specific battery. There is also a need for a battery charger which reduces the chance of overheating or overcharging the battery.